Variation-aware dynamic voltage/frequency scaling

Abstract

Fine-grained dynamic voltage/frequency scaling (DVFS) is an important tool in managing the balance between power and performance in chip-multiprocessors. Although manufacturing process variations are giving rise to significant core-to-core variations in power and performance, traditional DVFS controllers are unaware of these variations. Exploiting the different power/performance profiles of the cores can significantly improve energy-efficiency. Two hardware DVFS control algorithms are considered and the gains enabled by incorporating variability-awareness are demonstrated on multithreaded commercial workloads. For a design with per-core voltage/frequency islands (VFIs), the mean power per unit throughput for a simple threshold-based controller is reduced by 8.0% when variability-awareness is added. A complex greedy-search controller sees an even larger reduction of 15.4%. The variability-aware versions of the two controllers achieve power/throughput reductions of 2.1% and 9.9% relative to LinOpt, a recent software variability-aw are DVFS scheme. Designs which apply DVFS at a coarser granularity are also considered, and the variability-aware schemes maintain significant improvement over the -unaware ones. With four cores per VFI, variability-awareness reduces power/throughput by 6.5% and 9.2% for the threshold- based and greedy-search controllers, respectively.